This invention relates to a laboratory calendering machine for comparing different calendering techniques, for example in connection with gradient calendering. Furthermore, said machine provides means for studying the effects calendering has on different parameters and variables related to paper or board or any other web material, for example on qualities such as roughness, gloss, strength, stiffness, moisture content and optical properties. Effects on other special properties, for example blistering tendency of coated paper, may also be studied.
Previously known laboratory calendering devices have only been designed for carrying out tests on individual socalled laboratory sheets. A known laboratory calendering device has consisted of a frame in which two nip forming rolls have been mounted. In order to steady the feeding of the sheets, a feeding table has usually been arranged in front of the nip formed between the two rolls. Understandably, feeding speed and the speed by which the sheet passes between the rolls has been slow and thus not comparable with a working speed of an actual production calender. This has restricted the use of such a known device as a research device. Moreover, when using a soft roll, the sheets cause damage to the roll. Consequently, test results have been of limited use and tend to be unreliable.